This invention relates to a molding apparatus for providing a toothed wheel, a toothed pulley or the like by means of pressing work. More particularly, the invention relates to a molding apparatus in which a pressing machine uses a stacked array of molding dies having different tooth heights from one die to the next to form highly accurate teeth on the cylindrical wall portion of a bottomed cylindrical body with a single press-molding stroke.
Two manners are employed conventionally to form teeth on an intermediate product which is cylindrical in shape. One manner is to form the teeth by extrusion molding, and the other is to form the teeth in small increments by means of drawing. With the extrusion manner, however, the entire height of a tooth is molded at one time in a single die. This causes the molded tooth to sag to a large degree, and/or to form draw or shrinkage marks at the corner portions of the tooth, making it impossible to obtain a tooth of the prescribed shape. Consequently, in order to prevent such sagging as well as the formation of draw or shrinkage marks, the thickness of the cylindrical wall portion of the starting stock is enlarged with respect to the thickness of the tooth portion, but this greatly increases the molding load. The result is scoring of the die and molded surface, which in turn roughens the face of the molded tooth and shortens the life of the mold or dies to a great extent.
With the drawing manner, on the other hand, scoring does not occur since drawing is carried out by a stroke applied in small increments. This is disadvantageous, however, in that costs are raised owing to a prolonged molding operation and an increase in mold or die up-keep costs.